Photometer.



Patented May 24, 1910.

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l D A UNITED STATES PATENT oEEIoE.

HAAKON BRYHNI, OF BGBSEN, NEAR TRONDHJEM, NORWAY.

PHOTOMETER.

To all whom it may concern:

Be it known that I, HAAKoN BRYI-INI, a subject of the King of Norway,residing at Borsen, near Trondhjem, Norway, have invented certain newand useful Improvements in Photometers; and I do hereby declare thefollowing to be a full, clear, and exact description of the invention,such as will enable others skilled in the art to which it appertains tomake and use the same, reference being had to the accompanying drawings,and to letters of reference marked thereon, which form a part of thisspecification.

My invention relates to a device for indicating the intensity of light,commonly known as a photometer, and is especially adapted to determinethe time of exposure of a photographic plate or film.

In my photometer, I make use of the Wellknown fact that the diameter ofthe pupil of the human eye changes rapidly according to the intensity oflight, to which the eye is subjected.

In the drawing, Figure 1 is a perspective view of one form of the newapparatus, while Fig. 2 is a section through the same; Fig. 3 is asection through another form of the apparatus.

A is a mirror and B a lens, preferably a plane-convex lens, the flatface being the upper face. On this upper face of the lens a scale C ismarked in the glass. The mirror A and the lens B are mounted in parallelplates of a folding frame D, as sometimes used for magnifying glasses.

In the use of the apparatus, one eye is held close to the lens B. Theenlarged image of the pupil of the eye and the scale C will be reflectedin the mirror A, and the diameter of the pupil can be directly measuredby the scale C. If desired, a table for calculating the time of exposurefor a cer- Specification of Letters Patent.

Application filed August 29, 1907.

Patented May 24, 1910.

Serial No. 390,627.

tain kind of plate or film and a certain size of blender may be attachedto the frame I).

The apparatus shown in Fig. 2 consists of a box F, which is closed sothat no light can enter it except through the opening G, which is closedby a glass plate H. The box is provided with a second opening E, which,however, is closed by a diaphragm I. When the box F is held with theopening G tight against one eye, no light can reach the eye, and thepupil therefore will assume its largest size. \Vhen, however, thediaphragm I is gradually opened, light will be admitted to the interiorof the box through the opening E, and, consequently, the pupil willsuccessively grow smaller, which can be observed in the mirror A. Theglass H is provided with two marks C. When the pupil has grown to assumea diameter equal to the distance between these two marks, the size ofthe opening uncovered by the diaphragm I will indicate the intensity ofthe light. This method is an indirect way of measuring the size of thepupil.

Claims.

1. In a photometer the combination of a mirror, and a transparent bodymounted at a fixed distance from said mirror and having marks thereon tobe reflected in the said mirror together with an image of the pupil.

2. In a photometer the combination of a mirror, and a lens mounted at afixed distance from said mirror, the said lens being provided with marksto be reflected in the said mirror together with an image of the pupilof the eye.

In testimony that I claim the foregoing as my invention, I have signedmy name in presence of two subscribing Witnesses.

HAAKON BRYHNI.

Witnesses:

SVIRRE BERG,

WV. RoMINo.

